In Situ Oxidative\nRing-Opening of Calix[8]arene to\nConstruct Stable Bismuth-Oxo Clusters with Exposed Catalytic Sites\nfor Specific Electroreduction of CO<sub>2</sub> to HCOOH

Nanocluster catalysts typically face challenges in balancing\nstability\nwith catalytic efficiency. This study introduces a unique bismuth-oxo\ncluster, solely protected by two ring-opened calixarenes, which demonstrates\nnot only enhanced structural stability but also superior catalytic\nperformance in the sustained conversion of CO<sub>2</sub> to HCOOH\nvia electrocatalysis. For the first time, we reveal that under specific\nsolvothermal conditions, <i>tert</i>-butylcalix[8]arene\n(TBC[8]) can undergo in situ oxidative cleavage of its C–C\nbond, leading to ring-opened polyphenolic molecules. These molecules\nserve as protective ligands for the bismuth-oxo cluster, bestowing\nexceptional structural stability and offering a more flexible and\ndiverse configuration compared to intact TBC[8]. This adaptability\npromotes the exposure of active bismuth sites on the cluster surface,\nenhancing catalytic efficiency. Notably, the <b>Bi</b><sub><b>10</b></sub> cluster, featuring a monobismuth active site, achieves\nan exceptional formate production efficiency of 98.79% at −1.25\nV vs RHE while maintaining superb durability over 8 h. The stability\nand catalytic processes of <b>Bi</b><sub><b>10</b></sub> surpass those of the <b>Bi</b><sub><b>13</b></sub> cluster,\nwhich is structurally reinforced by two intact TBC[8] molecules and\nstabilized by four benzoic ligands. Through in situ infrared spectroscopy\nand density functional theory calculations, we demonstrate that the\nmonobismuth active site in <b>Bi</b><sub><b>10</b></sub> more effectively stabilizes the *OCHO intermediate, thereby promoting\nthe electrocatalytic reduction of CO<sub>2</sub> to HCOOH compared\nto <b>Bi</b><sub><b>13</b></sub>. This comparative performance\nunderscores the potential of ring-opened calixarene ligands in enhancing\nthe functionality of nanocluster catalysts.